1. Field of the Invention
This invention relates to semiconductor electronic devices, and more particularly to vertical channel silicon carbide metal-oxide-semiconductor field effect transistors having low parasitic resistance.
2. Description of the Related Art
Silicon carbide (SiC) devices have intrinsic advantages for microwave power and low frequency power conditioning applications. For example, SiC has a high field saturation velocity which is three times larger than that of gallium arsenide (GaAs). Additionally, SiC has a high intrinsic critical breakdown field which is ten times higher than that of GaAs, and SiC has a high thermal conductivity which is ten times as high as that of GaAs.
One concern when using SiC devices in microwave and low frequency power applications is that the resistance between a metal contact and a heavily doped epitaxial layer of SiC is orders of magnitude higher than the resistance between a metal contact and heavily doped silicon. Conventional electronic device structures and planar ion implanted device structures should reduce parasitic resistances by increasing the doping concentration of the n+ contact regions to very high levels. The main difficulty with all devices in which the current flows horizontally near the surface is that current crowding occurs at the edge of the contact. The spreading resistance in the current crowded region increases the impedance in that region.